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Slow download speeds in Ubuntu 7.10

Posted on 2007-12-03
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Last Modified: 2013-12-14
I have a Ubuntu 7.10 server with 2 NICs acting as the router/firewall for a small LAN connected to a Billion 5200 ADSL2+ DSL "modem". The connection is advertized as 24/3Mbit, the actual negotiated connection speed at the moment is  19187/2235kbit. The router/firewall software in use is Shorewall 3.4.4. I'm using traffic shaping for upstream, prioritizing interactive traffic (ssh/rdp/etc), pings, tcp acks etc, obviously no shaping for downstream traffic.

The connection "seems" to otherwise work normally, upstream speeds are what I expect them to be, but downstream it seems like getting around 200kb/s over a single connection is the maximum, that is, around 10% of what it should be. If I have several simultaneous connections open, the speed goes up to around 700-800kb/s max, which is still just a bit over 1/3rd of what it should be. In Ubuntu 7.04 (and other distros before that) the speeds were what they were supposed to, around 1600-2000kb/s. All the hardware is still identical, including cables and such. The external connection (eth0) is autonegotiated to 100/FD, which is what the DSL box supports.

Any ideas what could be causing this and where should I start troubleshooting?
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Question by:CoccoBill
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Expert Comment

by:WizRd-Linux
ID: 20407363
Make sure that your "traffic" shaping isn't occuring on your downstream as well, it may be without you realising it.

Also, you may be limited by the site you are getting the data from.  Also check the MTU size isn't above 1500, if in doubt manually set it.

What is your download speed like getting data from say Microsoft or Apple, they are the two highest bandwidth sites I can think of at the moment.
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by:CoccoBill
ID: 20407495
Traffic shaping isn't active for the downstream, unless shorewall is doing something funky. Actually shorewall might quite well be the culprit here, since the distro upgrade also updated to a new major version of it, something might have gone awry with the upgrade. My MTU is 1500 and the speeds I mentioned I'm getting are the same from all sources (connexion, akamai, local unis...).

I think I'll try reinstalling shorewall from a clean slate without TC to make sure that isn't the problem, what other things should I check?
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WizRd-Linux earned 500 total points
ID: 20407845
If the shorewall interface isn't giving you specific information it may pay to login to the console and check iptables to see if it is marking inbound packets.

A linux box, shorewall or not will always allow transmitting and receiving of packets as fast as the link will allow unless the packets are being mangled and fed to a daemon that shapes the packets, or QOS.

As previously mentioned, it sounds like your inbound traffic is being shared and each individual connection is being shaped to approximately 5% of the avaliable bandwidth.
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by:CoccoBill
ID: 20409722
How would I do that and what should I look for?
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by:CoccoBill
ID: 20463796
It was indeed the traffic shaping causing the problems. It wasn't marking any downstream packets, but for some reason the priorization doesn't work the way it should. Turning the TC script off immediately bounces the dl speed back to where I expect it to be. Here are the rules I was using:

tcclasses:
#INTERFACE      MARK    RATE    CEIL            PRIORITY        OPTIONS
eth0            1       full/8  full/4          1               tcp-ack,tos-min
eth0            2       full/4  full            2
eth0            3       full/2  full            3               default
eth0            4       full/8  full*9/10       4

- Tcp acks, icmp ping and tos-minimize-delay has 1st priority with 12.5% minimum, 25% maximum of the full upstream bandwidth.
- Priority 2 is all interactive traffic (ssh/irc/msn/rdp/etc) with min 25%, max 100%.
- Priority 3 is all traffic nor fitting to any other class (ie. default) with min 50%, max 100%.
- Priority 4 is for all upstream file transfers, scp/ftp/etc. with min 12.5%, max 90%.

This used to work perfectly, as in being able to download at full speed, upload at close to max speed while all interactive connections remained fully responsive. Any idea why it wouldn't work anymore? Clearly seems like the upstream traffic is suddenly drastically hindering downstream traffic. I couldn't find anything obvious in the Shorewall version notes/documentation.
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Expert Comment

by:WizRd-Linux
ID: 20474947
Unfortunately I have never used TC on linux before, I hope another expert can possible offer a solution for you.
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Author Closing Comment

by:CoccoBill
ID: 31412388
Thanks for your help, still haven't figured out what was wrong with the TC but at least the speeds otherwise are back to normal.
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